1. Field of the Invention
The present invention relates to a color coated expanded polystyrene substrate.
More particularly, the present invention relates to a coating composition for use in producing such a polystyrene substrate.
Still more particularly, the present invention relates to a coating composition and a method of color coating an expanded polystyrene drop-out ceiling tile, by which its heat shrinking drop-out characteristic is preserved.
2. Description of the Prior Art
Suspended ceilings of translucent or opaque plastic panels are regularly installed in commercial buildings to conceal ducts, wiring, piping, lighting fixtures and the like, as well as for decorative purposes. Such a plastic ceiling panel or tile must conform to certain fire standards. If the ceiling tile conceals a heat activated sprinkler system, it must quickly react to heat by "shrinking" so as to "drop out" of its setting in the event of fire, thereby exposing the automatic sprinkler system located above the suspended ceiling. Such a panel, moreover, should not be flammable in the event of fire, and it should not contribute fuel nor generate smoke.
Uncoated expanded polystyrene board stock prepared by foaming polystyrene beads in a conventional manner has been found to possess these various properties and has, accordingly, received the approval of the Factory Mutual System as meeting its standards for use in suspended ceilings where fire sprinkler systems are employed (Factory Mutual Approval Guide Supplement II 1982, page 32, "Suspended Ceilings Plastic"). Expanded polystyrene ceiling panels, therefore, are widely accepted and used particularly in commercial buildings where product conformity with Factory Mutual System standards is essential. The natural color of expanded polystyrene board stock, however, is opaque white, which renders ceiling panels made from such stock unusable, or at least undesirable, for installations where a colored ceiling is required or desired. Unfortunately, it is very difficult, because of the cellular wall structure of expanded polystyrene, to coat it without significantly etching and damaging its surface. This difficulty, moreover, is aggravated in the instance of ceiling tiles or panels since the coating must not only not damage the surface of the panel, but must also not harm the drop-out or heat shrink properties of the expanded polystyrene which make it acceptable for suspended ceiling installation. The coating must not insulate the polystyrene; an insulating affect would detrimentally affect its heat shrink capability. Similarly, if the coating strengthens or reinforces the ceiling tile, the heat shrink characteristics will also be adversely affected.
Attempts have been made to paint or otherwise color coat expanded polystyrene drop-out ceiling tiles, but without success, principally because the drop-out characteristic of the uncoated polystyrene is altered beyond acceptable standards. These color coating attempts, moreover, have entailed procedural requirements of such cost, especially when applied to surfaces of large areas, as to make them prohibitive as a practical matter even if they were technically successful.